Large-diameter, high-torque end mill (and similar) tools present a difficult problem relating to suitable holders or holding assemblies. Such tools must be held firmly against axial pullout forces and radial rotational forces, with a minimum amount of looseness between tool and holder when secured. Further, the tool should be easily and quickly inserted into and secured within the holder and the tool shank required should be of a design conventional to commercially-available end mill (or similar) tools.
The prior art tool holders for such tools has suggested two divergent generic approaches to the problem, neither of which is entirely satisfactory. The first approach uses a collet and chuck assembly, with the tool and collet held in place within the chuck body by frictional forces resulting from tightening of a collet nut. This approach provides the desired centering ability through the collet action but has a limited resistance to rotational forces, since the collet may be rotated within the chuck (and the tool shank within the collet) by a rather low rotational force.
By adding a non-pullout feature or assembly as described in the referenced Non-Pullout Collet Patent, the resistance of the tool shank to rotation with respect to the collet is improved. Other prior art systems have set screws or tangs coupled between the collet and shank to retain the tool shank within the collet. Such screws or tangs resist tool rotation with respect to the collet; however, none of these prior art techniques provides a rotationally-resistance connection from the tool shank to the chuck body (and through the collet). A direct connection between the chuck body and the tool shank is desirable, however, for maximum effectiveness in transmitting driving force. Further, a frictional retaining force may be degraded somewhat by industrial contaminants (oils, etc.) which lubricate the connection, reducing friction therebetween and the retaining force.
The other generic approach eliminates the collet altogether and provides a mounting of the tool to the chuck through the provision of one or more set screws within the chuck and used with or without special-made grooves in the tool shank. This approach is undesirable because the special tool shank grooves require customizng of each tool. Also, the lack of a collet in this assembly eliminates two advantages of a collet: a convenient and quick way of eliminating the clearance necessary for tool insertion; and centering device within the chuck. Both of these advantages of a collet enable precision machining by the entire machine and, therefore, the assemblies without a collet have inherent limitations regarding the precision (or tolerances) to which the machining can be held.
Further, in both of the generic approaches of the prior art, the tool must be positioned within a precise rotational orientation which may be troublesome, difficult or time consuming.
Therefore, it is apparent that the prior art tool holders for high torque end mill and similar tools present undesirable disadvantages and limitations.